Made the function opt_sum_query to return HA_ERR_KEY_NOT_FOUND when
no matches were found (instead of -1 it returned prior this patch).
This changes allow us to avoid possible conflicts with return values
from user-defined handler methods which also may return -1. 
No particular test cases are provided with this fix.


sql/opt_sum.cc:
  Fixed bug #24987.
  Made the function opt_sum_query to return HA_ERR_KEY_NOT_FOUND when
  no matches were found (instead of -1 it returned prior this patch).
  This changes allow us to avoid possible conflicts with return values
  from user-defined handler methods which also may return -1.
sql/sql_select.cc:
  Fixed bug #24987.
  Made the function opt_sum_query to return HA_ERR_KEY_NOT_FOUND when
  no matches were found (instead of -1 it returned prior this patch).
  This changes allow us to avoid possible conflicts with return values
  from user-defined handler methods which also may return -1.